The present invention relates generally to support columns for chairs, tables and the like, and more particularly, to a novel apparatus and method for mounting a support column to a chair base and chair tilt-control housing.
It is well known in the prior art that a support column can be used to interconnect an object to be supported, such as a chair seat, and a supporting structure, such as a chair base. In general, the support column carries the load imposed by the object being supported and transfers it to the supporting structure. The use of a simple support column thereby eliminates the need for multiple load bearing members. There are many types of commercial support columns currently used in a variety of applications. For example, a simple rigid member of fixed height can be interposed between a chair seat and base to provide support. This type of support member is embodied, for example, in a typical bar stool. More recently, support columns have been made height-adjustable, thereby giving the user more flexibility in their use of the object. For example, a height-adjustable chair can accommodate users of different heights when accessing a fixed elevation work station. Alternatively, a single user can adjust the height of the chair to access work stations of varying elevation.
Typically, height-adjustable support columns include telescopically movable tubular members. For example, a support column can include a guide tube attached to the chair base and a telescopic tube attached to the seat. A piston-cylinder type gas spring is used to actuate the telescopic tube, thereby raising or lowering the seat according to the user's preference. For example, one such support column is described in U.S. Pat. No. 4,580,749, issued Apr. 8, 1986, and entitled Support Column Unit.
As stated previously, the load imposed by the seat must be transferred to the support column, which in turn, transfers it to the base. To effectuate this load transfer properly, it is important to have the seat and base firmly mounted to the support column. Typically, the support column is inserted in a cavity located in the base. To allow for proper load transfer, the support column is typically press fitted into the cavity by applying a static force to the column while providing for an opposing reaction force against the base. Conversely, the static force can be applied to the base while supporting the support column. Alternatively, an impact force can be applied by a human operator wielding a rubber mallet or other impact type device.
Similar to the base, a chair seat typically has a hub adapted for mounting the seat to the support column. Alternatively, some chairs are designed to allow the user to tilt the chair. Such tilt-chairs typically have a tilt control housing and mechanism which support the chair seat as shown in U.S. Pat. No. 5,333,368, issued Aug. 2, 1994, and entitled Chair Control With Forward Tilt. The tilt-control housing generally has a hub and a core adapted for mounting to the support column. As with the base, the tilt control housing is press fitted onto the support column by applying either a static or impact force, while providing for an opposing reaction force.
The aforementioned method of mounting the support column to the tilt control housing and base has several disadvantages. First, when human operators manually apply the impact force to the support column, base or tilt control housing, there is necessarily a lack of uniformity in the amount of force applied to each chair being assembled. Therefore, some support columns may be more firmly mounted in the base and tilt-control housing than others. Moreover, since a separate static or impact force is used to mount each of the base and tilt-control housing to the support column, each base or tilt-control housing can be mounted more or less firmly than the other on any particular chair. Furthermore, the two-step process of mounting the support column on the base and then mounting the tilt control housing to the support column is time consuming and inefficient, thereby increasing the costs of manufacturing.